Sleep apnea treatment apparatus with reset feature

ABSTRACT

Improved methodology and apparatus for the clinical study and treatment of sleep apnea which incorporates one or more of the following features: (1) application of mono-level, alternating high and low level, or variable positive airway pressure generally within the airway of the patient with the mono-level, high and low level, or variable airway pressure generally being coordinated with and/or responsive to the spontaneous respiration of the patient, (2) usage of adjustably programmable pressure ramp circuitry capable of producing multiple pressure ramp cycles of predetermined duration and pattern whereby the ramp cycles may be customized to accommodate the specific needs of an individual sleep apnea patient so as to ease the patient&#39;s transition from wakefulness to sleep, (3) remote control or patient-sensed operation of the apparatus, (4) employment of safety circuitry, reset circuitry and minimum system leak assurance circuitry, controls and methods, and (5) utilization of clinical control circuitry whereby sleep disorder data may be compiled and appropriate therapy implemented during a one-night sleep study.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.08/110,372 filed Aug. 23, 1993 (now U.S. Pat. No. 5,551,418), whichitself is a continuation-in-part of U.S. patent application Ser. No.07/786,269 filed Nov. 1, 1991 (originally issued as U.S. Pat. No.5,239,995 and now reissued as Re. 35,295).

FIELD OF THE INVENTION

The present invention relates generally to methodology and apparatus fortreatment of sleep apnea and, more particularly, to mono-level, bi-leveland variable positive airway pressure apparatus, as well as feedbacktype versions thereof, including circuitry for enabling a patient toselectively actuate one or more pressure ramp cycles wherein, duringeach ramp cycle, available airway pressure increases with time from apredetermined minimum pressure value to a prescription pressure, therebyfacilitating the patient's transition from a waking to a sleeping state.

BACKGROUND OF THE INVENTION

The sleep apnea syndrome afflicts an estimated 1% to 5% of the generalpopulation and is due to episodic upper airway obstruction during sleep.Those afflicted with sleep apnea experience sleep fragmentation andintermittent, complete or nearly complete cessation of ventilationduring sleep with potentially severe degrees of oxyhemoglobindesaturation. These features may be translated clinically into extremedaytime sleepiness, cardiac arrhythmias, pulmonary-artery hypertension,congestive heart failure and/or cognitive dysfunction. Other sequelae ofsleep apnea include right ventricular dysfunction with cor pulmonale,carbon dioxide retention during wakefulness as well as during sleep, andcontinuous reduced arterial oxygen tension. Hypersomnolent sleep apneapatients may be at risk for excessive mortality from these factors aswell as by an elevated risk for accidents while driving and/or operatingpotentially dangerous equipment.

Although details of the pathogenesis of upper airway obstruction insleep apnea patients have not been fully defined, it is generallyaccepted that the mechanism includes either anatomic or functionalabnormalities of the upper airway which result in increased air flowresistance. Such abnormalities may include narrowing of the upper airwaydue to suction forces evolved during inspiration, the effect of gravitypulling the tongue back to appose the pharyngeal wall, and/orinsufficient muscle tone in the upper airway dilator muscles. It hasalso been hypothesized that a mechanism responsible for the knownassociation between obesity and sleep apnea is excessive soft tissue inthe anterior and lateral neck which applies sufficient pressure oninternal structures to narrow the airway.

The treatment of sleep apnea has included such surgical interventions asuvulopalatopharyngoplasty, gastric surgery for obesity, andmaxillo-facial reconstruction. Another mode of surgical interventionused in the treatment of sleep apnea is tracheostomy. These treatmentsconstitute major undertakings with considerable risk of postoperativemorbidity if not mortality. Pharmacologic therapy has in general beendisappointing, especially in patients with more than mild sleep apnea.In addition, side effects from the pharmacologic agents that have beenused are frequent. Thus, medical practitioners continue to seeknon-invasive modes of treatment for sleep apnea with high success ratesand high patient compliance including, for example in cases relating toobesity, weight loss through a regimen of exercise and regulated diet.

Recent work in the treatment of sleep apnea has included the use ofcontinuous positive airway pressure (CPAP) to maintain the airway of thepatient in a continuously open state during sleep. For example, U.S.Pat. No. 4,655,213 and Australian patent AU-B-83901/82 both disclosesleep apnea treatments based on continuous positive airway pressureapplied within the airway of the patient.

Also of interest is U.S. Pat. No. 4,773,411 which discloses a method andapparatus for ventilatory treatment characterized as airway pressurerelease ventilation and which provides a substantially constant elevatedairway pressure with periodic short term reductions of the elevatedairway pressure to a pressure magnitude no less than ambient atmosphericpressure.

U.S. Pat. No. 5,199,424 and published PCT Application No. WO 88/10108describes a CPAP apparatus which includes a feedback system forcontrolling the output pressure of a variable pressure air sourcewhereby output pressure from the air source is increased in response todetection of sound indicative of snoring. According to additionalembodiments of the apparatus disclosed in these references, a pressureramp cycle (i.e., a gradual increase in output pressure) may occur uponinitial activation of the apparatus which gradually increases outputpressure from a predetermined minimum to a predetermined maximum ortherapeutic pressure specifically selected for the patient.

Publications pertaining to the application of CPAP in treatment of sleepapnea include the following:

1. Lindsay, D A, Issa F G, and Sullivan C. E. "Mechanisms of SleepDesaturation in Chronic Airflow Limitation Studied with Nasal ContinuousPositive Airway Pressure (CPAP), "Am Rev Respir Dis, 1982; 125: p. 112.

2. Sanders N H, Moore S E, Eveslage J. "CPAP via nasal mask: A treatmentfor occlusive sleep apnea, Chest, 1983; 83: pp. 144-145.

3. Sullivan C E, Berthon-Jones M. Issa F G. "Remission severeobesity-hypoventilation syndrome after short-term treatment during sleepwith continuous positive airway pressure, Am Rev Respir Dis, 1983; 128:pp. 177-181.

4. Sullivan C E, Issa F G, Berthon-Jones M., Eveslage J. "Reversal ofobstructive sleep apnea by continuous positive airway pressure appliedthrough the nares, Lancet, 1981; 1: pp. 862-865.

5. Sullivan C E, Berthon-Jones M. Issa F G. "Treatment of obstructiveapnea with continuous positive airway pressure applied through the nose.Am Rev Respir Dis, 1982; 125: p. 107. Annual Meeting Abstracts.

6. Rapoport D M, Sorkin B, Garay S M, Goldring R N. "Reversal of the`Pickwickian Syndrome` by long-term use of nocturnal nasal-airwaypressure," N Engl J. Med, 1982; 307: pp. 931-933.

7. Sanders M H, Holzer B C, Pennock B E. "The effect of nasal CPAP onvarious sleep apnea patterns, Chest, 1983; 84: p. 336. Presented at theAnnual Meeting of the American College of Chest Physicians, ChicagoIll., October 1983.

8. Sanders, M H. "Nasal CPAP Effect on Patterns of Sleep Apnea", Chest,1984; 86: 839-844.

Although mono-level positive airway pressure or CPAP has been found tobe very effective and well accepted, it suffers from some of the samelimitations, although to a lesser degree, as do the surgery options;specifically a significant proportion of sleep apnea patients do nottolerate CPAP well. Thus, development of other viable non-invasivetherapies has been a continuing objective in the art.

SUMMARY OF THE INVENTION

The present invention contemplates a novel and improved method fortreatment of sleep apnea as well as novel methodology and apparatus forcarrying out such improved treatment method. The invention contemplatesthe treatment of sleep apnea through application of pressure at variancewith ambient atmospheric pressure within the upper airway of the patientin a manner to promote patency of the airway to thereby relieve upperairway occlusion during sleep.

In a first embodiment of the invention, positive pressure is applied ata substantially constant, patient-specific prescription pressure withinthe airway of the patient to maintain -he requisite patent or "splint"force to sustain respiration during sleep periods. This form oftreatment is commonly known as mono-level CPAP therapy.

In another embodiment of the invention, pressure is applied alternatelyat relatively higher and lower prescription pressure levels within theairway of the patient so that the pressure-induced patent force appliedto the patients airway is alternately a larger and a smaller magnitudeforce. The higher and lower magnitude positive prescription pressurelevels, which will be hereinafter referred to by the acronyms IPAP(inspiratory positive airway pressure) and EPAP (expiratory positiveairway pressure), may be initiated by spontaneous patient respiration,apparatus preprogramming, or both, with the higher magnitude pressure(IPAP) being applied during inspiration and the lower magnitude pressure(EPAP) being applied during expiration. This method of treatment maydescriptively be referred to as bi-level therapy. In bi-level therapy,it is EPAP which has the greater impact upon patient comfort. Hence, thetreating physician must be cognizant of maintaining EPAP as low as isreasonably possible to maintain sufficient pharyngeal patency duringexpiration, while optimizing user tolerance and efficiency of thetherapy.

This latter embodiment contemplates a novel and improved apparatus whichis operable in accordance with a novel and improved method to providesleep apnea treatment. More specifically, a flow generator and anadjustable pressure controller supply air flow at a predetermined,adjustable pressure to the airway of a patient through a flowtransducer. The flow transducer generates an output signal which is thenconditioned to provide a signal proportional to the instantaneous flowrate of air to the patient. The instantaneous flow rate signal is fed toa low pass filter which passes only a signal indicative of the averageflow rate over time. The average flow rate signal typically would beexpected to be a value representing a positive flow as the system islikely to have at least minimal leakage from the patient circuit (e.g.,small leaks about the perimeter of the respiration mask worn by thepatient). The average flow signal is indicative of such leakage becausethe summation of all other components of flow over time must beessentially zero since inspiration flow must equal expiration flowvolume over time, that is, over a period of time the volume of airbreathed in equals the volume of the gases breathed out.

Both the instantaneous flow signal and the average flow rate signal arefed to an inspiration/expiration decision module which is, in itssimplest form, a comparator that continually compares the input signalsand provides a corresponding drive signal to the pressure controller. Ingeneral, when the instantaneous flow exceeds average flow, the patientis inhaling and the drive signal supplied to the pressure controllersets the pressure controller to deliver air, at a preselected elevatedpressure, to the airway of the patient. Similarly, when theinstantaneous flow rate is less than the average flow rate, the patientis exhaling and the decision circuitry thus provides a drive signal toset the pressure controller to provide a relatively lower magnitude ofpressure in the airway of the patient. The patient's airway thus ismaintained open by alternating higher and lower magnitudes of pressurewhich are applied during spontaneous inhalation and exhalation,respectively.

As has been noted, some sleep apnea patients do not tolerate standard,i.e., mono-level, CPAP therapy. Specifically, approximately 25% ofpatients cannot tolerate CPAP due to the attendant discomfort. StandardCPAP mandates equal pressures (i.e., a single prescription pressure)during both inhalation and exhalation. The elevated pressure during bothphases of breathing may create difficulty in exhaling and the sensationof an inflated chest. However, we have determined that although bothinspiratory and expiratory air flow resistances in the airway areelevated during sleep preceding the onset of apnea, the airway flowresistance may be less during expiration than during inspiration. Thusit follows that the bi-level therapy of our invention as characterizedabove may be sufficient to maintain pharyngeal patency during expirationeven though the pressure applied during expiration is not as high asthat needed to maintain pharyngeal patency during inspiration. Inaddition, some patients may have increased upper airway resistanceprimarily during inspiration with resulting adverse physiologicconsequences. Thus, our invention also contemplates applying elevatedpressure only during inhalation thus eliminating the need for global(inhalation and exhalation) increases in airway pressure. The relativelylower pressure applied during expiration may in some cases approach orequal ambient pressure. The lower pressure applied in the airway duringexpiration enhances patient tolerance by alleviating some of theuncomfortable sensations normally associated with CPAP.

Under prior CPAP therapy, pressures as high as 20 cm H₂ O have beenrequired, and some patients on nasal CPAP thus have been needlesslyexposed to unnecessarily high expiratory pressures with the attendantdiscomfort and elevated mean airway pressure, and theoretic risk ofbarotrauma. Our invention permits independent application of a higherinspiratory airway pressure in conjunction with a lower expiratoryairway pressure in order to provide a therapy which is better toleratedby the 25% of the patient population which does not tolerate CPAPtherapy, and which may be safer and more comfortable in the other 75% ofthe patient population.

As has been noted hereinabove, the switch between higher and lowerprescription pressure magnitudes can be controlled by spontaneouspatient respiration, apparatus preprogramming, or both. Hence, themanufacturer or the clinician can govern respiration rate and volume or,alternatively, this capability may be independently ascribed to thepatient. As has been also noted, the invention contemplates automaticcompensation for system leakage whereby nasal mask fit and air flowsystem integrity are of less consequence than in the prior art. Inaddition to the benefit of automatic leak compensation, other importantbenefits of the invention include lower mean airway pressures for thepatient and enhanced safety, comfort and tolerance.

In all embodiments, the present invention makes use of "ramp" circuitryoperatively connected to pressure control means of the apparatus andselectively activatable by the patient to effect at least one pressure"ramp cycle" which is described in greater detail below. The maximumduration(s) of the ramp cycle(s), the shape(s) of the ramp curve(s) andthe prescription pressure(s) are normally established by a sleep studyof the patient and this data can be programmed into the apparatus of theinstant invention. It is also desirable that the apparatus be operableeither by manual controls located directly on the apparatus or viaremote control.

Approximately 25% of all patients who undergo CPAP therapy for sleepapnea experience respiration discomfort and find it difficult to fallasleep because of the therapy. The purpose of a ramp cycle is toalleviate this discomfort. A ramp cycle is an automatic cycle that, onceactivated, causes the apparatus (mono-level, bi-level or variable) tooutput a predetermined minimum positive pressure at or above ambientpressure which is gradually increased over a predetermined time periodknown as "ramp time" during which the patient begins to fall asleep.Upon expiration of the ramp time the patient typically has fallen asleepand at such time the pressure produced by the apparatus is that of thepatient's therapy prescription pressure(s) whereupon the patientreceives normal treatment as he sleeps.

A particular advantage of the present invention is that the unique rampcircuitry enables not only an initial ramp cycle to be achieved for whenone first attempts to sleep but such circuitry also permits one or moreadditional cycles to be selectively activated by the user at instanceswhere the user awakens during an extended rest period, or when the userfails to fall asleep during the first ramp cycle and again requires aramp cycle to fall back to sleep, or even within (i.e., during) analready ongoing ramp cycle. Typically, during a sleeping period ofseveral hours, the time required to once again fall asleep after brieflybeing awakened is generally less than the time spent initially fallingasleep. To accommodate this phenomenon, the ramp circuitry of theinstant invention allows adjustment of the ramp time of any additionalramp cycle to run for a selected fraction of the initial ramp time,which itself may be a pre-programmed, patient-selected aclinician-selected fraction of a prescription time preset by a healthcare professional in supervision of the patient's sleep apnea treatment.

The ramp circuitry enables a physician or other health care worker toset the initial ramp time(s) and prescription pressure(s). Additionally,however, the novel ramp circuitry of the present invention permitsadjustment of the "shape" of the pressure ramp curve, whereby thephysician, health care worker or patient can suitably manipulateappropriate controls associated with the ramp circuitry to control thepressure output pattern of the ramp (as represented as a function ofpressure versus time) such that it may assume virtually anyconfiguration including, inter alia, linear, stepped, or curvilinearslope, depending upon a patient's particular needs as dictated by theresults of the patient's sleep study. In the case of bi-level systemsaccording to the instant invention, the ramp circuitry also affords, forexample, simultaneous, independent, identical or differential ramping ofIPAP and EPAP. Alternatively, the parameters establishable by the rampcircuitry may also be preprogrammed by the manufacturer.

Additionally, sufferers of sleep apnea are sometimes afflicted by othermaladies which limit the degree to which they may safely physicallyexert themselves. An advantage of the present invention is that itenables a limited-mobility user, at his discretion, to operate theapparatus either by manual controls located directly on the apparatus orvia remote control. Equally as important, it provides any sleep apneasufferer using the apparatus with the peace of mind of knowing that thepressure can be reduced at any time via the remote control. Further, thepreferred embodiment of the remote control contemplated for use in thepresent invention is one which the user can operate easily and reliablyeither in light or darkness to turn the apparatus on and off as well asselectively activate the first or subsequent ramp cycles.

As additional or alternative design features, the apparatus may includean automatic ON/OFF mechanism and/or alternative ramp activation means.

The automatic ON/OFF mechanism desirably comprises a sensor meanssituated within or proximate to the patient's breathing circuit. Suchbreathing circuit will be understood to include, but is not limited to,the gas flow conduit, the gas flow generator means and the respiratoryinterface, e.g., oral mask, nasal mask, oral/nasal mask, endotrachealtube, nasal cannulae, or other suitable appliance. The sensor means mayassume the form of a pressure, flow, thermal, audio, optic, electricalcurrent, voltage, force, displacement or other suitable transducer whichdetects the presence (and/absence) of the patient. More particularly,according to a first mode of operation, when the respiratory interfaceis appropriately positioned over the patient's face, the sensor meanswill operate so as to detect at least one of the above-mentionedconditions indicative of the patient's presence and generate a signalthat is transmitted to the flow generator to activate the apparatus. Ina second mode of operation, the sensor means may be designed solely forapparatus activation purposes. Hence, upon removal of the respiratoryinterface, the sensor means would fail to detect any conditionsindicative of the patient's presence and, therefore, generate anappropriate signal to deactivate the apparatus. A third mode ofoperation combines these functions. That is, the sensor means may beoperable to detect both the presence and absence of the patient andgenerate a signal to activate the apparatus upon detection of acondition indicative of the patient's presence, as well as an apparatusdeactivation signal upon failure of detecting such a condition, i.e.,the patient's absence.

The alternative ramp activation means may comprise a sensor meansresponsive to signals of selected magnitude and/or frequency consciouslyproduced by the patient. In accordance with a presently preferredembodiment, the alternative ramp activations means may comprise apressure transducer, for instance, a microphone located within or nearthe patient's respiratory interface, associated gas flow conduit or gasflow generator and capable of detecting sound of a limited frequencyrange spanning that associated with human speech. So configured, thetransducer would be nonresponsive to common ambient sounds produced bythe user (e.g., coughing or sneezing), machinery noise, music or animalsounds. Moreover, by being isolated through its enclosure within the gasflow system, the transducer would detect only the patient's speech tothe exclusion of others in the vicinity or speech emanating fromtelevision or radio sources. Upon detection of the patient's speech suchas, for example, when the patient awakens and speaks to start a new rampcycle, the audio transducer generates and transmits an activation-signalto the ramp circuitry to initiate the desired ramp cycle. The sensor mayalternatively be operable to begin a ramp cycle in response to detectionof a predetermined pattern of inhalations and/or exhalations or otherconscious actions by the patient.

As noted hereinabove, the ramp circuitry, remote or automatic ON/OFFmechanisms and/or remote or pressure responsive ramp activation meansmay be incorporated and utilized with success in mono-level, bi-leveland variable positive airway pressure ventilation apparatus orpatient-responsive feedback type versions thereof, an example of oneversion of which will be described in greater detail hereinafter. Otherembodiments of the invention employ novel system control circuitryincluding reset circuitry, safety circuitry, therapy delay circuitryand/or minimum system leakage assurance circuitry which may also be usedin conjunction with mono-level, bi-level and variable level ventilationapparatus, but find especially beneficial application with feedback typeversions of those ventilation apparatus because of their particularmanner of operation.

Briefly, the system reset circuitry permits the patient (if suddenlyawakened, for example) to instantaneously reset the system outputpressure to a predetermined reduced pressure after which the treatmentmay then proceed as it did prior to reset. An advantage attendant toboth the ramp circuitry and reset circuitry is that they both afford thepatient the opportunity to immediately respire against a reducedpressure once awakened, thereby enhancing patient comfort and transitionback to a sleeping state. Unlike the ramp circuitry, however, the resetcircuitry permits the patient to more rapidly receive the full benefitsof the positive airway pressure therapy since therapy resumesinstantaneously upon reset. Such modality, as will be appreciated, ismore likely to be exercised by a patient who generally experienceslittle difficulty in falling back to sleep after being awakened duringan extended period of sleep.

The safety circuitry of the present invention allows the patient or hisoverseeing health care professional to establish minimum and maximumsystem output pressures below and above which the system will notdispense pressurized gas. The minimum pressure will, of course, be atleast zero and, preferably, a threshold pressure sufficient to maintainpharyngeal patency during expiration. The maximum pressure, on the otherhand, will be some pressure somewhat less than that which would resultin over-inflation and perhaps rupture of the patient's lungs. The safetycircuitry functions differently than the prescription pressure controlsof the ramp circuitry. That is, instead of establishing lower and upperprescription pressures to be applied during normal usage of theapparatus it sets absolute minimum and maximum fail-safe output pressurelimits which will not be exceeded, and therefore potentially causephysical harm to the patient, in the event other system componentsmalfunction.

The therapy delay circuitry proposed herein permits a patient to bediagnosed and treated during a single sleep study. Typically, thepractice has been for the patient to undergo two sleep studies at anappropriate observation facility such as a hospital, clinic orlaboratory. The first night is spent observing the patient in sleep andrecording selected parameters such as oxygen saturation, chest wallabdominal movement, air flow, expired CO₂, ECG, EEG, EMG and eyemovement. This information can be interpreted to diagnose the nature ofthe sleeping disorder and confirm the presence or absence of apnea and,where present, the frequency of apneic episodes and extent and durationof associated oxygen desaturation. Apneas can be identified asobstructive, central or mixed.

The second night is spent with the patient undergoing nasal positiveairway pressure therapy. When apnea is observed the pressure setting isincreased as required to determine the maximum pressure necessary toprevent apnea. As for determining the minimum pressure required toprevent occlusions, for a given patient in a given physical conditionthere normally will be found different minimum pressures for variousstages of sleep. Thus, the appropriate minimum pressure discovered inthe laboratory is necessarily the maximum of all minimum pressuresrecorded for that particular night and may not necessarily be the idealminimum pressure for all occasions.

The therapy delay circuitry of the instant invention is operable tosuppress the therapy for any desired period of time while associateddata storage and retrieval means compile data associated with selectedones of the patient's physiological parameters to be used for diagnosisof the patient's particular sleep disorder. Once sufficient data isrecorded, system control adjustments based upon the data may be inputtedas appropriate and the therapy delay circuitry may be switched from itstherapy suppression mode to a therapy application mode, wherebytreatment specifically adapted and responsive to the patient's observedphysiological condition may be effectively implemented in a single nightin the sleep study facility. With the costs of daily hospital andrelated medical stays ever on the rise, the advantage of reducing thelength of the patient's sleep study to potentially half of whatotherwise would be required is self-evident.

The present invention also provides for minimum system leakage assurancecircuitry, the function of which is to assure that the system dischargesa minimum leakage flow during therapy, i.e., when the patient is asleepor attempting to fall asleep. The minimum system leakage assurancecircuitry desirably comprises an adjustable leakage test pressurecontrol, an adjustable pre-therapy pressure control, an adjustabletimer, and a switch. The switch is responsive to the timer and triggersthe leakage test pressure control to transmit a signal causing theapparatus to output a preset leakage test pressure. The switch is alsooperable to trigger the pre-therapy pressure control to transmit asignal causing the apparatus to output a preset pre-therapy pressure.The preset leakage test pressure may be the peak pressure output by theapparatus during the previous night or some other desired pressure,whereas the pre-therapy pressure may be the minimum pressure output bythe apparatus during the previous night or some other pressure.

Using the timer, after the apparatus is activated the system will outputthe leakage test pressure to temporarily overpressurize the gas flowcircuit for some preselected period of time. This time period willnormally be sufficient for the patient to properly position and seal themask on his face and adjust any gas conduit connections such that systemleakage flow is brought to a minimum. After the passage of theprescribed time period, the timer triggers the switch to activate thepre-therapy pressure control, thereby causing the system to output theselected pre-therapy pressure for a specified duration also establishedby the timer. After expiration of the designated time for pre-therapypressure application, the timer then urges the switch to assume aneutral position whereby the apparatus outputs its mono-level, bi-levelor variable ventilation pressure therapy.

An advantage of such an arrangement is that by temporarilyoverpressurizing the gas flow circuit prior to treatment, unwantedsystem leaks can be discovered and sealed before the patient fallsasleep. Hence, leakage flow (or average system flow). and its associatedpressure can be minimized while the patient sleeps, thereby enhancingpatient comfort. In lieu of or addition to the timer, the minimum systemleakage assurance circuitry may also include a low leak detector. Thelow leak detector detects whether the system, under the application theleak test pressure, outputs a leakage flow less than a predeterminedminimum. If a sufficiently low leakage flow is detected, the low leakdetector automatically overrides the timer and triggers the pre-therapypressure control to cause the system to output the specified pre-therapypressure for the preset time and then output the appropriate therapypressure.

Similarly, in addition to or in lieu of the timer and/or the low leakdetector, the minimum system leakage assurance circuitry may include amanual override, e.g., an audio transducer, which responds to patientinitiated commands to override the timer in a manner similar to the lowleak detector.

Other details, objects and advantages of the present invention willbecome apparent as the following description of the presently preferredembodiments and presently preferred methods of practicing the inventionproceeds.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more readily apparent from the followingdescription of preferred embodiments thereof shown, by way of exampleonly, in the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an apparatus according to theinstant invention;

FIG. 2 is a functional block diagram showing an alternative embodimentof the invention;

FIG. 3 is a functional block diagram of the Estimated Leak Computer ofFIG. 2;

FIG. 4 is a frontal elevation of a control panel for a first embodimentof the apparatus of this invention;

FIG. 5 is a functional block diagram of a further embodiment of anapparatus according to the instant invention;

FIG. 5A is a functional block diagram of a further embodiment of anapparatus according to the instant invention;

FIG. 6 is a functional block diagram of a further embodiment of anapparatus according to the instant invention;

FIG. 7A is a flow diagram of a first embodiment of programmable rampcontrol circuitry of the instant invention suitable for use inrespiratory system ventilation apparatus;

FIG. 7B is a flow diagram of a further embodiment of programmable rampcontrol circuitry of the instant invention suitable for use inrespiratory system ventilation apparatus;

FIGS. 8A, 8B and 8C reveal three examples of typical ramp curve shapesthat may be achieved via the programmable ramp circuitry of FIG. 7;

FIGS. 9A, 9B, 9C, 9D, 9E and 9F illustrate representative IPAP and EPAPramping operations;

FIG. 10 is a functional block diagram of a further embodiment of anapparatus according to the instant invention;

FIG. 11 is a functional block diagram of a further embodiment of anapparatus according to the instant invention;

FIG. 12 is a functional block diagram of a further embodiment of anapparatus according to the instant invention;

FIG. 13 is a functional block diagram of a further embodiment of anapparatus according to the instant invention;

FIG. 14 is a functional block diagram of a further embodiment of anapparatus according to the instant invention; and

FIG. 15 is a functional block diagram of a further embodiment of anapparatus according to the instant invention.

DETAILED DESCRIPTION OF THE INVENTION

There is generally indicated at 10 in FIG. 1 an apparatus according toone presently preferred embodiment of the instant invention and shown inthe form of a functional block diagram. Apparatus 10 is operableaccording to a novel process which is another aspect of the instantinvention for delivering breathing gas such as air alternately atrelatively higher and lower pressures (i.e., equal to or above ambientatmospheric pressure) to a patient 12 for treatment of-the conditionknown as sleep apnea.

Apparatus 10 comprises a gas flow generator 14 (e.g., a blower) whichreceives breathing gas from any suitable source, a pressurized bottle 16or the ambient atmosphere, for example. The gas flow from flow generator14 is passed via a delivery conduit 20 to a breathing appliance such asa mask 22 of any suitable known construction which is worn by patient12. The mask 22 may preferably be a nasal mask or a full face mask asshown. Other breathing appliances which may be used in lieu of a maskinclude nasal cannulae, an endotracheal tube, or any other suitableappliance for interfacing between a source of breathing gas and apatient.

The mask 22 includes a suitable exhaust port means, schematicallyindicated at 24, for exhaust of breathing gases during expiration.Exhaust port 24 preferably is a continuously open port which imposes asuitable flow resistance upon exhaust gas flow to permit a pressurecontroller 26, located in line with conduit 20 between flow generator 14and mask 22, to control the pressure of air flow within conduit 20 andthus within the airway of the patient 12. For example, exhaust port 24may be of sufficient cross-sectional flow area to sustain a continuousexhaust flow of approximately 15 liters per minute. The flow via exhaustport 24 is one component, and typically the major component of theoverall system leakage, which is an important parameter of systemoperation. In an alternative embodiment to be discussed hereinbelow, ithas been found that a non-rebreathing valve may be substituted for thecontinuously open port 24.

The pressure controller 26 is operative to control the pressure ofbreathing gas within the conduit 20 and thus within the airway of thepatient. Pressure controller 26 is located preferably, although notnecessarily, downstream of flow generator 14 and may take the form of anadjustable valve which provides a flow path which is open to the ambientatmosphere via a restricted opening, the valve being adjustable tomaintain a constant pressure drop across the opening for all flow ratesand thus a constant pressure within conduit 20.

Also interposed in line with conduit 20, preferably downstream ofpressure controller 26, is a suitable flow transducer 28 which generatesan output signal that is fed as indicated at 29 to a flow signalconditioning circuit 30 for derivation of a signal proportional to theinstantaneous flow rate of breathing gas within conduit 20 to thepatient.

It will be appreciated that flow generator 14 is not necessarily apositive displacement device. It may be, for example, a blower whichcreates a pressure head within conduit 20 and provides air flow only tothe extent required to maintain that pressure head in the presence ofpatient breathing cycles, the exhaust opening 24, and action of pressurecontroller 26 as above described. Accordingly, when the patient isexhaling, peak exhalation flow rates from the lungs may far exceed theflow capacity of exhaust port 24. As a result, exhalation gas back flowswithin conduit 20 through flow transducer 28 and toward pressurecontroller 26, and the instantaneous flow rate signal from transducer 28thus will vary widely within a range from relatively large positive(i.e., toward the patient) flow to relatively large negative (i.e., fromthe patient) flow.

The instantaneous flow rate signal from flow signal conditioningcircuitry 30 is fed as indicated at 32 to a decision module 34, a knowncomparator circuit for example, and is additionally fed as indicated at36 to a low pass filter 38. Low pass filter 38 has a cutoff frequencylow enough to remove from the instantaneous flow rate input signal mostvariations in the signal which are due to normal breathing. Low passfilter 38 also has a long enough time constant to ensure that spurioussignals, aberrant flow patterns and peak instantaneous flow rate valueswill not dramatically affect system average flow. That is, the timeconstant of low pass filter 38 is selected to be long enough that itresponds slowly to the instantaneous flow rate signal input.Accordingly, most instantaneous flow rate input signals which could havea large impact on system average flow in the short term have a muchsmaller impact over a longer term, largely because such instantaneousflow rate signal components will tend to cancel over the longer term.For example, peak instantaneous flow rate values will tend to bealternating relatively large positive and negative flow valuescorresponding to peak inhalation and exhalation flow achieved by thepatient during normal spontaneous breathing. The output of low passfilter 38 thus is a signal which is proportional to the average flow inthe system, and this is typically a positive flow which corresponds toaverage system leakage (including flow from exhaust 24) since, as noted,inhalation and exhalation flow cancel for all practical purposes.

The average flow signal output from the low pass filter 38 is fed asindicated at 40 to decision circuitry 34 where the instantaneous flowrate signal is continually compared to the system average flow signal.The output of the decision circuitry 34 is fed as a drive signalindicated at 42 to control the pressure controller 26. The pressuremagnitude of breathing gas within conduit 20 thus is coordinated withthe spontaneous breathing effort of the patient 12, as follows.

When the patient begins to inhale, the instantaneous flow rate signalgoes to a positive value above the positive average flow signal value.Detection of this increase in decision circuitry 34 is sensed at thestart of patient inhalation. The output signal from decision circuitry34 is fed to pressure controller 26 which, in response, provides higherpressure gas flow within conduit 20 and thus higher pressure within theairway of the patient 12. This is the higher magnitude pressure value ofour bi-level system and is referred to hereinbelow as IPAP (inhalationpositive airway pressure). During inhalation, the flow rate withinconduit 20 will increase to a maximum and then decrease as inhalationcomes to an end.

At the start of exhalation, air flow into the patient's lungs is nil andas a result the instantaneous flow rate signal will be less than theaverage flow rate signal which, as noted is a relatively constantpositive flow value. The decision circuitry 34 senses this condition atthe start of exhalation and provides a drive signal to pressurecontroller 26 which, in response, provides gas flow within conduit 20 ata lower pressure which is the lower magnitude pressure value of thebi-level system, referred to hereinbelow as EPAP (exhalation positiveairway pressure). As has been noted hereinabove the range of EPAPpressures may include ambient atmospheric pressure. When the patientagain begins spontaneous inhalation, the instantaneous flow rate signalagain increases over the average flow rate signal, and the decisioncircuitry once again feeds a drive signal to pressure controller 26 toreinstitute the IPAP pressure.

System operation as above specified requires at least periodiccomparison of the input signals 32 and 40 by decision circuitry 34.Where this or other operations are described herein as continual, thescope of meaning to be ascribed includes both continuous (i.e.,uninterrupted) or periodic (i.e., at discrete intervals).

As has been noted, the system 10 has a built-in controlled leakage viaexhaust port 24 thus assuring that the average flow signal will be atleast a small positive flow. During inhalation, the flow sensed by theflow transducer will be the sum of exhaust flow via port 24 and allother system leakage downstream of transducer 28, and inhalation flowwithin the airway of the patient 12. Accordingly, during inhalation theinstantaneous flow rate signal as conditioned by conditioning module 30,will reliably and consistently reflect inhalation flow exceeding theaverage flow rate signal. During exhalation, the flow within conduit 20reverses as exhalation flow from the lungs of the patient far exceedsthe flow capacity of exhaust port 24. Accordingly, exhalation airbackflows within conduit 20 past transducer 28 and toward pressurecontroller 26. Since pressure controller 26 is operable to maintain setpressure, it will act in response to flow coming from both the patientand the flow generator to open an outlet port sufficiently toaccommodate the additional flow volume and thereby maintain thespecified set pressure as determined by action of decision circuitry 34.

In both the inhalation and exhalation cycle phases, the pressure of thegas within conduit 20 exerts a pressure within the airway of the patientto maintain an open airway and thereby alleviate airway constriction.

In practice, it may be desirable to provide a slight offset in theswitching level within decision circuitry 34 with respect to the averageflow rate signal, so that the system does not prematurely switch fromthe low pressure exhalation mode to the higher pressure inhalation mode.That is, a switching setpoint offset in the positive direction fromsystem average flow may be provided such that the system will not switchto the IPAP mode until the patient actually exerts a significantspontaneous inspiratory effort of a minimum predetermined magnitude.This will ensure that the initiation of inhalation is completelyspontaneous and not forced by an artificial increase in airway pressure.A similar switching setpoint offset may be provided when in the IPAPmode to ensure the transition to the lower pressure EPAP mode will occurbefore the flow rate of air into the lungs of the patient reaches zero(i.e., the switch to EPAP occurs slightly before the patient ceasesinhalation.) This will ensure that the patient will encounter no undueinitial resistance to spontaneous exhalation.

From the above description, it will be seen that a novel method oftreating sleep apnea is proposed according to which the airway pressureof the patient is maintained at a higher positive pressure duringinspiration and a relatively lower pressure during expiration, allwithout interference with the spontaneous breathing of the patient. Thedescribed apparatus is operable to provide such treatment for sleepapnea patients by providing a flow of breathing gas to the patient atpositive pressure, and varying the pressure of the air flow to providealternately high and low pressure within the airway of the patientcoordinated with the patient's spontaneous inhalation and exhalation.

To provide pressure control, the flow rate of breathing gas to thepatient is detected and processed to continually provide a signal whichis proportional to the instantaneous breathing gas flow rate in thesystem. The instantaneous flow rate signal is further processed toeliminate variations attributable to normal patient respiration andother causes thus generating a signal which is proportional to theaverage or steady state system gas flow. The average flow signal iscontinually compared with the instantaneous flow signal as a means todetect the state of the patient's spontaneous breathing versus averagesystem flow. When instantaneous flow exceeds the average flow, thepatient is inhaling, and in response the pressure of gas flowing to thepatient is set at a selected positive pressure, to provide acorresponding positive pressure within the airway of the patient. Whencomparison of the instantaneous flow rate signal with the average flowsignal indicates the patient is exhaling, as for example when theinstantaneous flow signal indicates flow equal to or less than theaverage flow, the pressure of breathing gas to the patient is adjustedto a selected lower pressure to provide a corresponding lower pressurewithin the airway of the patient.

In an alternative embodiment of the invention as shown in FIGS. 2 and 3,the low pass filter 38 is replaced by an estimated leak computer whichincludes a low pass filter as well as other functional elements as shownin FIG. 3. The remainder of the system as shown in FIG. 2 is similar inmost respects to the system shown in FIG. 1. Accordingly, like elementsare identified by like numbers, and the description hereinabove of FIG.1 embodiment also applies generally to FIG. 2.

By using the operative capability of the estimated leak computer 50, asdescribed hereinbelow, it is possible to adjust the reference signalwhich is fed to decision circuitry 34 on a breath by breath basis ratherthan merely relying on long term average system flow. To distinguishthis new reference signal from average system flow it will he referredto hereinbelow as the estimated leak flow rate signal or just theestimated leak signal.

As was noted hereinabove, the average system flow rate reference signalchanges very slowly due to the long time constant of the low pass filter38. This operative feature was intentionally incorporated to avoiddisturbance of the reference signal by aberrant instantaneous flow ratesignal inputs such as erratic breathing patterns. While it was possibleto minimize the impact of such aberrations on the average flow ratereference signal, the average flow signal did nevertheless change,although by small increments and only very slowly in response todisturbances. Due to the long time constant of the low pass filter, suchchanges in the reference signal even if transitory could last for a longtime.

Additionally, even a small change in the reference signal could producea very significant effect on system triggering. For example, since theobjective is to trigger the system to the IPAP mode when inhalation flowjust begins to go positive, small changes in the reference signal couldresult in relatively large changes in the breathing effort needed totrigger the system to IPAP mode. In some instances the change inreference signal could be so great that with normal breathing effort thepatient would be unable to trigger the system. For example, if thesystem were turned on before placement of the mask on the face of thepatient, the initial free flow of air from the unattached mask couldresult in a very large magnitude positive value for initial averagesystem flow. If such value were to exceed the maximum inspiratory flowrate achieved in spontaneous respiration by the patient, the systemwould never trigger between the IPAP and EPAP modes because the decisioncircuitry would never see an instantaneous flow rate signal greater thanthe average flow rate signal, at least not until a sufficient number ofnormal breathing cycles after application of the mask to the patient tobring the reference signal down to a value more closely commensuratewith the actual system leak in operation. As has been noted, with thelow pass filter thus could take a rather long time, during which timethe patient would be breathing spontaneously against a uniform positivepressure. This would be tantamount to conventional mono-level CPAP andnot at all in keeping with the present invention.

In addition to the embodiment based on a reference signal derived fromestimated leak flow rate on a breath by breath basis which is controlledtotally by spontaneous patient breathing, two further modes of operationalso are envisioned, one being spontaneous/timed operation in which thesystem automatically triggers to the IPAP mode for just long enough toinitiate patient inspiration if the system does not sense inspiratoryeffort within a selected time after exhalation begins. To accomplishthis, a timer is provided which is reset at the beginning of eachpatient inspiration whether the inspiratory cycle was triggeredspontaneously or by the timer itself. Thus, only the start ofinspiration is initiated by the timer. The rest of the operating cyclein this mode is controlled by spontaneous patient breathing and thecircuitry of the system to be described.

A further mode of operation is based purely on timed operation of thesystem rather than on spontaneous patient breathing effort, but with thetimed cycles coordinated to spontaneous patient breathing.

Referring to FIG. 3, the estimated leak computer 50 includes the lowpass filter 38' as well as other circuits which are operative to makecorrections to the estimated leak flow rate signal based on ongoinganalysis of each patient breath. A further circuit is provided which isoperative to adjust the estimated leak flow rate signal quickly aftermajor changes in system flow such as when the blower has been runningprior to the time when the mask is first put on the patient, or after amajor leak the system has either started or has been shut off.

The low pass filter 38' also includes a data storage capability whosefunction will be described hereinbelow.

The low pass filter 38' operates substantially as described above withreference to FIG. 1 in that it provides a long term average of systemflow which is commensurate with steady state system leakage includingthe flow capacity of the exhaust port 24. This long term average isoperative in the FIG. 3 embodiment to adjust the estimated leak flowrate reference signal only when system flow conditions are changing veryslowly.

To provide breath by breath analysis and adjustment of the referencesignal, a differential amplifier 52 receives the instantaneous flow ratesignal as indicated at 54, and the estimated leak signal output from lowpass filter 38' as indicated at 56.

The output of differential amplifier 52 is the difference betweeninstantaneous flow rate and estimated leak flow rate, or, in otherwords, estimated instantaneous patient flow rate. This will be clearupon considering that instantaneous flow is the sum of patient flow plusactual system leakage. The estimated patient flow signal output fromdifferential amplifier 52 is provided as indicated at 58 to a flowintegrator 60 which integrates estimated patient flow breath by breathbeginning and ending with the trigger to IPAP. Accordingly, anadditional input to the flow integrator 60 is the IPAP/EPAP state signalas indicated at 62. The IPAP/EPAP state signal is the same as the drivesignal provided to pressure controller 26; that is, it is a signalindicative of the pressure state, as between IPAP and EPAP, of thesystem. The state signal thus may be used to mark the beginning and endof each breath for purposes of breath by breath integration byintegrator 60.

If the estimated leak flow rate signal from low pass filter 38' is equalto the true system leak flow rate, and if the patient's inhaled andexhaled volumes are identical for a given breath (i.e., total positivepatient flow equals total negative patient flow for a given breath),then the integral calculated by integrator 60 will be zero and noadjustment of estimated leak flow rate will result. When the integralcalculated by integrator 60 is nonzero, the integral value in the formof an output signal from integrator 60 is provided as indicated at 64 toa sample and hold module 66. Of course, even with a zero value integral,an output signal may be provided to module 66, but the ultimate resultwill be no adjustment of the estimated leak flow rate signal.

A nonzero integral value provided to module 66 is further provided tomodule 38' as indicated at 68 with each patient breath by operativeaction of the IPAP/EPAP state signal upon module 66 as indicated at 70.The effect of a nonzero integral value provided to module 38' is anadjustment of the estimated leak flow rate signal proportional to theintegral value and in the direction which would reduce the integralvalue towards zero on the next breath if all other conditions remain thesame.

With this system, if the patient's net breathing cycle volume is zero,and if the system leak flow rate changes, the integrator circuit willcompensate for the change in leak flow rate by incremental adjustmentsto the estimated leak flow rate within about ten patient breaths.

The integrator circuit 60 also will adjust the estimated leak flow ratesignal in response to nonzero net volume in a patient breathing cycle.It is not unusual for a patient's breathing volume to be nonzero. Forexample, a patient may inhale slightly more on each breath than heexhales over several breathing cycles, and then follow with a deeper orfuller exhalation. In this case, the integrator circuit would adjust theestimated leak flow rate signal as if the actual system leak rate hadchanged; however, since the reference signal correction is only aboutone tenth as large as would be required to make the total correction inone breath, the reference signal will not change appreciably over justone or two breaths. Thus, the integrator circuit accommodates bothchanges in system leakage and normal variations in patient breathingpatterns. The integrator circuit normally would be active, for example,during rapid patient breathing.

An end exhalation module 74 is operative to calculate another datacomponent for use in estimating the system leak flow rate as follows.The module 74 monitors the slope of the instantaneous flow rate waveform. When the slope value is near zero during exhalation (as indicatedby the state signal input 76) the indication is that the flow rate isnot changing. If the slope of the instantaneous flow rate signal waveform remains small after more than one second into the respiratoryphase, the indication is that exhalation has ended and that the net flowrate at this point thus is the leak flow rate. However, if estimatedpatient flow rate is nonzero at the same time, one component of theinstantaneous flow rate signal must be patient flow.

When these conditions are met, the circuit adjusts the estimated leakflow rate slowly in a direction to move estimated patient flow ratetoward zero to conform to instantaneous patient flow conditions expectedat the end of exhalation. The adjustment to estimated leak flow rate isprovided as an output from module 74 to low pass filter 38' as indicatedat 80. When this control mechanism takes effect, it disables the breathby breath volume correction capability of integrator circuit 60 for thatbreath only.

The output of module 74 is a time constant control signal which isprovided to low pass filter 38' to temporarily shorten the time constantthereof for a sufficient period to allow the estimated leak flow rate toapproach the instantaneous flow rate signal at that specific instant. Itwill be noted that shortening the low pass filter time constantincreases the rapidity with which the low pass filter output (a systemaverage) can adjust toward the instantaneous flow rate signal input.

Another component of estimated leak flow rate control is a gross errordetector 82 which acts when the estimated patient flow rate, providedthereto as indicated at 84, is away from zero for more than about 5seconds. Such a condition may normally occur, for example, when the flowgenerator 14 is running before mask 22 is applied to the patient. Thispart of the control system is operative to stabilize operation quicklyafter major changes in the leak rate occur.

In accordance with the above description, it will be seen that low passfilter 38' acts on the instantaneous flow rate signal to provide anoutput corresponding to average system flow, which is system leakagesince patient inspiration and expiration over time constitutes a netpositive flow of zero. With other enhancements, as described, the systemaverage flow can be viewed as an estimate of leakage flow rate.

The differential amplifier 52 processes the instantaneous flow ratesignal and the estimated leak flow rate signal to provide an estimatedpatient flow rate signal which is integrated and nonzero values of theintegral are fed back to module 38' to adjust the estimated leak flowrate signal on a breath by breath basis. The integrator 60 is reset bythe IPAP/EPAP state signal via connection 62.

Two circuits are provided which can override the integrator circuit,including end exhalation detector 74 which provides an output to adjustthe time constant of low pass filter 38' and which also is provided asindicated at 86 to reset integrator 60. Gross error detector 82 is alsoprovided to process estimated patient flow rate and to provide anadjustment to estimated leak flow rate under conditions as specified.The output of module 82 also is utilized as an integrator reset signalas indicated at 86. It will be noted that the integrator 60 is resetwith each breath of the patient if, during that breath, it is ultimatelyoverridden by module 74 or 82. Accordingly, the multiple resetcapabilities for integrator 60 as described are required.

In operation, the system may be utilized in a spontaneous or bi-leveltriggering mode, a spontaneous/timed or bi-level/timed (bi-level/T) modeor a purely timed mode of operation. In spontaneous operation, decisioncircuitry 34 continuously compares the instantaneous flow rate withestimated leak flow rate. If the system is in the EPAP state or mode, itremains there until instantaneous flow rate exceeds estimated leak flowrate by approximately 40 cc per second. When this transition occurs,decision circuitry 34 triggers the system into the IPAP mode for 150milliseconds. The system will then normally remain in the IPAP mode asthe instantaneous flow rate to the patient will continue to increaseduring inhalation due to spontaneous patient effort and the assistanceof the increased IPAP pressure.

After the transition to the IPAP mode in each breath, a temporary offsetis added to the estimated leak flow rate reference signal. The offset isproportional to the integral of estimated patient flow rate beginning atinitiation of the inspiratory breath so that it gradually increases withtime during inspiration at a rate proportional to the patient'sinspiratory flow rate. Accordingly, the flow rate level above estimatedleak flow needed to keep the system in the IPAP mode during inhalationdecreases with time from the beginning of inhalation and in proportionto the inspiratory flow rate. With this enhancement, the longer aninhalation cycle continues, the larger is the reference signal belowwhich instantaneous flow would have to decrease in order to trigger theEPAP mode. For example, if a patient inhales at constant 500 cc persecond until near the end of inspiration, a transition to EPAP willoccur when his flow rate drops to about 167 cc per second after onesecond, or 333 cc per second after two seconds, or 500 cc per secondafter three seconds, and so forth. For a patient inhaling at a constant250 cc per second, the triggers would occur at 83, 167 and 250 cc persecond at one, two and three seconds into IPAP, respectively.

In this way, the EPAP trigger threshold comes up to meet the inspiratoryflow rate with the following benefits. First, it becomes easier andeasier to end the inspiration cycle with increasing time into the cycle.Second, if a leak develops which causes an increase in instantaneousflow sufficient to trigger the system into the IPAP mode, this systemwill automatically trigger back to the EPAP mode after about 3.0 secondsregardless of patient breathing effort. This would allow thevolume-based leak correction circuit (i.e., integrator 60) to act as itis activated with each transition to the IPAP mode. Thus, if a leakdevelops suddenly, there will be a tendency toward automatic triggeringrather than spontaneous operation for a few breaths, but the circuitwill not be locked into the IPAP mode.

Upon switching back to the EPAP mode, the trigger threshold will remainabove the estimated leak flcw rate approximately 500 milliseconds toallow the system to remain stable in the EPAP mode without switchingagain while the respective flow rates are changing. After 500milliseconds, the trigger threshold offset is reset to zero to await thenext inspiratory effort.

The normal state for the circuit is for it to remain in the EPAP modeuntil an inspiratory effort is made by the patient. The automaticcorrections and adjustments to the reference signal are effective tokeep the system from locking up in the IPAP mode and to preventauto-triggering while at the same time providing a high level ofsensitivity to inspiratory effort and rapid adjustment for changing leakconditions and breathing patterns.

In the spontaneous/timed mode of operation, the system performs exactlyas above described with reference to spontaneous operation, except thatit allows selection of a minimum breathing rate to be superimposed uponthe spontaneous operating mode. If the patient does not make aninspiratory effort within a predetermined time, the system willautomatically trigger to the IPAP mode for 200 milliseconds. Theincreased airway pressure for this 200 milliseconds will initiatepatient inspiration and provide sufficient time that spontaneous patientflow will exceed the reference signal so that the rest of the cycle maycontinue in the spontaneous mode as above described. The breaths perminute timer is reset by each trigger to IPAP whether the transition wastriggered by the patient or by the timer itself.

In the timed operating mode, all triggering between IPAP and EPAP modesis controlled by a timer with a breath per minute control being used toselect a desired breathing rate from, for example, 3 to 30 breaths perminute. If feasible, the selected breathing rate is coordinated to thepatients spontaneous breathing rate. The percent IPAP control is used toset the fraction of each breathing cycle to be spent in the IPAP mode.For example, if the breaths per minute control is set to 10 breaths perminute (6 seconds per breath) and the percent IPAP control is set to33%, then the flow generator will spend, in each breathing cycle, twoseconds in IPAP and four seconds in EPAP.

FIG. 4 illustrates a control panel for controlling the system abovedescribed and including a function selector switch 88 which includesfunction settings for the three operating modes, namely, spontaneous (orbi-level), spontaneous/timed (or bi-level/timed), and timed, as abovedescribed. The controls for spontaneous mode operation include IPAP andEPAP pressure adjustment controls 90 and 92, respectively. These areused for setting the respective IPAP and EPAP pressure levels. In thespontaneous/timed mode of operation, controls 90 and 92 are utilized asbefore to set IPAP and EPAP pressure levels, and breaths per minutecontrol 94 additionally is used to set the minimum desired breathingrate in breaths per minute. In the timed mode of operation, controls 90,92 and 94 are effective, and in addition the per cent IPAP control 96 isused to set the time percentage of each breath to be spent in the IPAPmode.

Lighted indicators such as LED's 97, 98 and 100 are also provided toindicate whether the system is in the IPAP or EPAP state, and toindicate whether, in the spontaneous/timed (bi-level/timed) mode ofoperation, the instantaneous state of the system is spontaneousoperation or timed operation.

Additionally, it may be desirable to provide a flow compensation signalto pressure controller 26 as indicated at 102 in FIG. 2 to compensatefor flow resistance inherent in the circuit; a non-rebreathing valve maybe utilized in lieu of exhaust port 24 at mask 22, and the like.

Turning to FIG. 5, there is depicted a further embodiment of the presentinvention, herein designated by reference numeral 10'. This embodimentfunctions substantially as a mono-level CPAP apparatus wherein thepressures of the breathing gas flow supplied to the patients airway issubstantially constant except when ramp control circuitry means 104 or104', described below in connection with FIGS. 7A and 7B, is activatedby the patient, through manipulation of a suitable mechanical actuatorsuch as a switch, a button, or the like, provided on the housing of theapparatus 10' or on remote control 106 to produce one or more outputpressure "ramp cycles." As will be later described in greater detail,remote control 106 may also be operable to turn apparatus 10 "ON" and"OFF."

FIG. 5A illustrates alternative means for effecting selective activationof the aforesaid ramp cycles. Desirably, the alternative ramp activationmeans may comprise any suitable sensor means for detecting andresponding to predetermined signals consciously produced by the patient.In this regard, according to a presently preferred construction, theramp activation means comprises a sensor means 106' in the form of apressure transducer responsive to a pressure or pressures of selectedmagnitude and/or frequency. For instance, the pressure transducer may bea microphone located within or proximate the gas flow system orbreathing circuit (i.e., in or near the patient's respiratory interface,associated gas flow conduit or gas flow generator) and capable ofdetecting sound waves of a limited frequency range substantiallyspanning that associated with human speech. Constructed and arranged assuch, the transducer would be nonresponsive to common ambient soundsproduced by the patient (e.g., coughing or sneezing), machinery noise,music or animal sounds. Moreover, by being isolated through itsenclosure within the gas flow system, the transducer would detect onlythe patient's speech to the exclusion of others in the vicinity orspeech emanating from television or radio sources. Upon detection of thepatient's speech such as, for example, when the patient awakens and thenspeaks to initiate a new ramp cycle to facilitate transition to asleeping state, the transducer generates and transmits an activationsignal to the ramp circuitry 104,104' to initiate the desired rampcycle. The ramp activation sensor may alternatively be operable to begina ramp cycle in response to detection of a predetermined pattern ofinhalations and/or exhalations or other conscious actions by thepatient.

As a variant to a manually manipulable remote control power actuator,apparatus 10' may instead include an automatic "ON/OFF" mechanism toachieve the same result. According to a presently preferredconstruction, such mechanism may comprise a sensor means situated withinor proximate the patient's breathing circuit which circuit (as notedabove) comprises gas conduit 20, gas flow generator means 14 and asuitable respiratory interface such as mask 22. This sensor meansfunctions as a patient presence sensor and is identified by referencenumeral 107'. The "patient sensor means" sensor 107' may suitably assumethe form of a pressure, flow, thermal, audio, optic, electrical current,voltage, force or displacement transducer which detects the presence(and/or absence) of the patient. More particularly, according to a firstmode of operation, when the respiratory interface is appropriatelypositioned over the patient's face, the sensor will operate to detectthe patient's presence and generate a signal that is transmitted to theflow generator 14 to activate the apparatus. In a second modality, thepatient sensor means may function exclusively to deactivate theapparatus. Hence, upon removal of the respiratory interface, the sensorwould fail to detect any conditions indicative of the patient's presenceand, therefore, generate and transmit an appropriate signal todeactivate the apparatus. A third mode of operation combines thesefunctions. In other words, the patient sensor means 107' may be operableto detect both the presence and absence of the patient and generate asignal to activate the apparatus upon detection of a conditionindicative of the patient's presence, as well as an apparatusdeactivation signal upon failure of detecting such a condition, i.e.,the patient's absence.

The embodiment of the instant invention illustrated in FIG. 6 operatesmuch like the embodiment revealed in FIG. 1, i.e., a bi-level apparatus.Apparatus 10", however, like apparatus 10' shown in FIG. 5, alsoincludes remote control 106 and ramp control circuitry means 104 or104'. It will be understood that in lieu of remote control 106 apparatus10" may utilize a sensor means 106', e.g., a pressure transducer similarto the pressure transducer 106' described with respect to FIG. 5A, forthe purpose of ramp cycle activation. In addition, it will also beunderstood that if the remote control 106 is eliminated, the apparatusmay be activated and deactivated by appropriate signals generated bysuitable means such as patient sensor means 107' which are thentransmitted therefrom to the flow generator 14 as was also discussed inconnection with FIG. 5A.

According to the preferred embodiments, the ramp control circuitry means104 (FIG. 7A) or 104' (FIG. 7B) provides full prescription pressure onapparatus activation or "start up" and controls the parameters ofmagnitude, duration and pressure output pattern or "shape" of both theinitial ramp cycle and any additional ramp cycles. Unlike otherapparatus having ramp capability wherein a ramp cycle automaticallycommences upon apparatus start up, apparatus 10' or 10" incorporatingramp control circuitry means 104 or 104' outputs pressure at fullprescription pressure. (which is preset by the patient's overseeinghealth care professional) until conscious activation of the initial rampcycle by the patient. This allows the patient to check for system leaksimmediately following start up. Alternatively, ramp control circuitrymeans 104 or 104' may be configured with suitable signal detection meanswhereby it automatically commences a ramp cycle either upon apparatusstartup, after a preset delay, or upon detection of a substantiallystabilized average system leakage signal from low pass filter 38 (FIG.2) or a substantially stabilized estimated leak flow rate signal fromestimated leak computer 50 (FIG. 3) following placement of mask 22 onthe patient's face. The commonality to all embodiments of the rampcontrol circuitry means being, however, that at least those ramp cyclessubsequent to initial ramp cycle be selectively activatable by thepatient via means to be described hereinbelow. As will be more fullyappreciated from the following, the apparatus 10' or 10" equipped withramp control circuitry means 104 or 104' permits the patient to not onlycontrol the aforesaid parameters of the ramp cycles (which, to provideoptimum treatment effectiveness may need to be adjusted daily) but thecommencement times of the ramp cycles as well.

Turning first to FIG. 7A the ramp cycles produced by the ramp controlcircuitry means 104 are generated by using a clock 108 to drive acounter 110. The counter 110 increments for each rising edge of theclock 108 and the output of the counter, which is influenced by a numberof factors described hereinafter, is transmitted to a digital to analogconverter 112. Other suitable means, however, such as a microprocessormay be used in place of digital to analog convertor 112 if desired. Theanalog output of the converter is added at juncture 114 to the minimumpressure setting that is input via an adjustable minimum pressuresetting control 116 and thereafter transmitted to the pressurecontroller 26 to provide a pressure ramp cycle. Minimum pressure settingcontrol 116 is operable to establish a minimum ramp pressure of zero orgreater for ramping of standard CPAP and ramping of IPAP and/or EPAP inbi-level respiratory therapy.

As mentioned hereinabove as an alternative to sensor means 106', a rampactuator 118, typically a user-manipulable button, switch, or the like,may be operated to effect commencement of a ramp cycle, whether suchcycle be the initial or a subsequent cycle. One such ramp actuator isdesirably provided on both the apparatus 10' or 10" and the remotecontrol 106. A similar arrangement may also be employed for theapparatus power "ON/OFF" actuator. Whether provided on the remotecontrol or apparatus 10' or 10" it is preferred that the power actuator(not shown) be substantially different in physical configuration thanthat of the ramp actuator such that a patient is provided visual andtactile feedback and can readily and reliably identify and operate theactuators either by sight or sense of touch. For purposes ofillustration, both the power actuator and ramp actuator will beunderstood to be depressible buttons; however, their possible physicalmanifestations are not intended nor should they be construed to belimited exclusively thereto. Upon depression of the power actuatorbutton, a control logic means 120 selects the patient's prescriptionpressure as determined by the patient's sleep study as the start-uppressure. The prescription pressure is initially input by the physicianor other health care professional into the ramp control circuitry means104 via a prescription pressure setting control 122 which permitsestablishment and subsequent adjustment of the magnitude of theprescription pressure. The expression "prescription pressure" in thepresent context meaning, of course, a single prescription pressure inthe case of standard mono-level CPAP therapy and a bifurcatedprescription pressure (IPAP and EPAP) in respect to bi-level therapy. Aramp time setting control 124 such as, for example, a rotary switch orother suitable control, is also provided (preferably internally of theapparatus housing to prevent patient tampering) and it, too, is normallyset by the health care professional to establish the appropriate ramptime of the first ramp cycle of the apparatus 10' or 10", i.e., thatramp cycle which is employed when a patient first seeks to fall asleep,such as at bed time. The appropriate ramp time for the first ramp cycleis also determined from data gathered in connection with the patient'ssleep study. A typical duration or "ramp time" of the initial ramp cyclemay be up to as high as 45 minutes or even longer.

As the patient becomes gradually accustomed to using the apparatusand/or realizes benefits from the therapy, it is common for the patientto require less time to initially fall asleep when using the apparatusthan when the patient first began treatment. Consequently, when usingany apparatus equipped with the ramp control circuitry means of thepresent invention, a need occasionally arises for the initial ramp timesetting to be adjusted (typically to a lesser duration than thatinitially set by the health care professional). Since it is often timesinconvenient or impractical for the patient to meet with his or herhealth care professional for necessary readjustments of the ramp timesetting control 124, the ramp control circuitry means of the presentinvention further desirably comprises a percent ramp time settingcontrol 126 that is accessible by the patient and adjustable to producefor the initial ramp cycle a modified initial ramp time that is afraction of the initial ramp time last established by the health careprofessional via ramp time setting control 124. Percent ramp timesetting control 126, preferably a rotary switch or the like, isadjustable to produce initial ramp times ranging from a minimum of fromabout 0 to 20% up to and including a maximum of 100% of the initial ramptime preset by the health care professional.

Frequently, a patient awakens during a period of extended sleep for anynumber of reasons. And, as is generally the case, the time required fora patient to fall back to sleep once awakened is less than thatinitially required. To accommodate this particular phenomenon, the rampcontrol circuitry means 104 (and 104' of FIG. 7B) of the presentinvention preferably include an additional ramp(s) time setting control127 that is adjustable to produce in ramp cycles subsequent to theinitial ramp cycle (the duration of which is established by the settingof control 124 as modified by the setting of control 126) ramp timesranging from a minimum of from about 0 to 20% of the initial ramp cycletime up to and including a maximum of 100% of the initial ramp cycletime. The ramp circuitry control means 104 and 104' are thus designedsuch that upon activation of any ramp cycle subsequent to the initialramp cycle the apparatus 10' or 10" executes a ramp cycle lasting for aduration established by the setting of the additional ramp(s) timesetting control 127. Hence, the patient is not only assisted in fallingback to sleep by the gradual increase in pressure but also is morequickly treated by the beneficial prescription pressure once he doesagain fall asleep due to the generally shorter duration of thesubsequent ramp cycle(s) relative to the initial ramp cycle. Theadditional ramp(s) time setting control 127 is preferably readilyaccessible by the patient yet not in area where it is likely to beinadvertently bumped or changed.

Looking to FIG. 7A, it is revealed that the ramp control circuitry means104 also preferably include an adjustable ramp pressure output patterncontrol 128 for establishing a predetermined pattern of pressure outputfrom pressure controller 26 during progression in a ramp cycle from theminimum ramp pressure set by minimum pressure setting control 116 andthe maximum ramp pressure (prescription pressure) set by theprescription pressure setting control 122. In FIG. 7B, the virtualstructural and functional equivalent of ramp pressure output patterncontrol 128 is the first ramp pressure output pattern control 128'.Either of controls 128 or 128' are operable by the health careprofessional or the patient to establish the selected pattern by whichthe pressure controller 26 outputs pressurized air during any ramp cyclein the case of ramp control circuitry means 104 or during the first rampcycle in the case of ramp control circuitry means 104'. Thus, thecontrols 128 and 128' serve to establish the "shape" of the ramp curveas a function of output pressure versus ramp time. Because of controls128 and 128', essentially any desired pattern of ramp output pressuremay be selected, examples of which will be discussed later by referenceto FIGS. 8A, 8B and 8C. In further connection therewith, ramp circuitrycontrol means 104' of FIG. 7B is distinguished from ramp circuitrycontrol means 104 of FIG. 7A by virtue of an adjustable componentidentified as additional ramp(s) pressure output pattern control 130.The function of this particular control is to enable an operator to formthe pressure output pattern of ramp cycles subsequent to the initialramp cycle into a pattern different therefrom. To illustrate, theinitial ramp pattern established by the first ramp pressure outputpattern control 128' may be, for example, substantially linear in slope,whereas the subsequent ramp pattern established by the additionalramp(s) pressure output pattern control 130 may be, inter alia,curvilinear or stepped in slope. The first ramp pressure output patterncontrols 128, 128' as well as the additional ramp(s) pressure outputpattern control 130 are adjustable to select patterns of the initial andsubsequent pressure ramps for standard mono-level CPAP and for IPAP andEPAP in bi-level CPAP treatment.

The operation of ramp circuitry control means 104 is essentially asfollows. Once the apparatus 10' or 10" within which means 104 isincorporated is powered and discharging pressurized air at prescriptionpressure, a first depression of ramp actuator button 118 (or detectionby sensor means 106' of predetermined signals consciously produced bythe patient) results in transmission of a signal to control logic means120 causing the control logic means to commence a first ramp cycle. Whenactivated, the first ramp cycle effects a drop in output pressure to theminimum pressure setting determined by the position of minimum pressuresetting control 116 (typically approximately 2.5 cm H₂ O) over a periodof up to 5 seconds (normal motor-blower run down). Upon reaching theminimum pressure, the output pressure from pressure controller 26 beginsto increase and continues to increase for the period of time assigned bythe ramp time setting control 124 as modified by percent ramp control126 in accordance with the predetermined pattern dictated by the ramppressure output control 128 until the prescription pressure is attained.Thereafter, the output pressure remains at the prescription pressure inthe mono-level apparatus 10' depicted in FIG. 5, while in bi-levelapparatus 10" shown in FIG. 6 the prescription pressure fluctuatesbetween the IPAP and EPAP pressures.

Upon a second or any subsequent depression of the ramp actuator button118 (or subsequent detection of predetermined signals by sensor means106') there is transmitted to the control logic means 120 a signaldirecting same to commence another ramp cycle whose duration isdetermined not only by the setting of the ramp time setting control 124and percent ramp time setting control 126 but also by that of theadditional ramp(s) time setting control 127, the influence of suchcontrol 127 being selectively overridden by control logic means 120during the initial ramp cycle. It will be appreciated that the patternor shape of the pressure output curve of any additional ramp cycle isdetermined by the setting of ramp pressure output pattern control 128except that such pattern will be compressed in proportion to thefraction of the initial ramp time chosen by the setting of theadditional ramp(s) time setting control 127.

The ramp control circuitry means 104' illustrated in 7B operatesessentially identically to its counterpart of FIG. 7A, the primarydifference being that ramp control circuitry means 104', via theadditional ramp(s) pressure output pattern control 130, enables thepressure pattern of the second and any other additional ramp cycles todiffer from that of the initial ramp cycle. As an example, where thefirst ramp pressure output pattern control 128' may be adjusted so as toproduce a substantially linear slope output pressure pattern, theadditional ramp(s) pressure output pattern control 130 may beselectively adjusted so as produce a stepped, curved or still otherpressure output pattern different from the substantially linear slope ofthe first ramp cycle, as may be desired or necessary.

FIG. 8A, 8B and 8C reveal exemplary shapes of pressure output patternswhich may be selected for the first 132 and subsequent 134 ramp cycles,namely, substantially linear slope in FIG. 8A, curvilinear in FIG. 8Band stepped in FIG. 8C. It will be appreciated that the pressure outputpatterns may assume virtually any desired configuration to best suit aparticular patient's requirements and, as noted hereabove, the secondand subsequent ramp patterns may differ from their associated initialramp cycles.

While not exhaustively illustrated to depict all possible scenarios,FIGS. 9A, 9B, 9C, 9D, 9E and 9F are included to show a representativesampling of IPAP and EPAP ramping operations in bi-level therapy whichare achievable through appropriate utilization of ramp control circuitrymeans 104,104'. For instance, FIG. 9A graphically shows a situationwhere the relative ramp shapes, magnitudes and durations of the IPAP andEPAP ramps are identical and simultaneous. Although their minimum ramppressures differ. FIG. 9B reflects a condition wherein the IPAP and EPAPramps have the same minimum pressure value and duration but differ inshape or slope. FIG. 9C represents IPAP and EPAP ramps having equalminimum ramp pressures and slopes but different durations. In FIG. 9Donly EPAP is ramped and in FIG. 9E only IPAP is ramped. FIG. 9Fpossesses characteristic traits of both FIGS. 9A and 8C. That is,similar to those shown in FIG. 9A, the relative ramp shapes, magnitudesand durations of the IPAP and EPAP ramps are identical and simultaneous.And, like the ramp configurations of FIG. 8C, the ramps of FIG. 9F alsoinclude stepped portions, although the generally steady-pressure step islocated at the beginning rather than at an intermediate stage of theramp cycle. Other relative IPAP and EPAP ramp arrangements will bereadily appreciated by those skilled in the subject art. Hence, the rampcurves shown in FIGS. 9A-9F should merely be viewed as illustrative butnot limitative of the feasible configurations of IPAP and EPAP rampsconsidered to be within the operational capacities of the ramp controlcircuitry means 104,104'. Furthermore, it will also be understood thatthe IPAP and EPAP ramp configurations displayed in FIGS. 9A-9F are notrepresentative of any specific ramp cycle. Thus, theirs and related rampcycles may be incorporated into the first and/or any subsequent rampcycles.

FIGS. 10 through 15 bring to light additional features and embodimentsof the present invention. Although the various system control circuitsdisclosed therein are depicted for illustrative purposes as being usedin conjunction with a feedback type positive airway pressure ventilationapparatus (in part because they are well suited to the particularoperational characteristics of such apparatus), it will be understoodthat the control circuits disclosed in these figures (or theirequivalents) may also be incorporated into non-feedback type mono-level,bi-level and variable positive airway pressure apparatus generally ofthe kinds described hereinabove.

Turning to FIG. 10, where like references represent elements similar tothose thus far discussed (as is also the case in the remaining views),there is generally indicated by reference numeral 210 a functional blockdiagram of a feedback-type positive airway pressure ventilationapparatus which constitutes another presently preferred embodiment ofthe instant invention. The general characteristics of the feedbackcircuit portion of the apparatus 210 is, per se, known in the art; see,for example, U.S. Pat. No. 5,199,424. Moreover, the essential componentsof the feedback circuit are common to FIGS. 10 through 15 and thefollowing structural and functional description of such circuit isapplicable to FIGS. 11 through 15 as well as to FIG. 10.

Like all embodiments heretofore described, apparatus 210 includes amotor driven flow generator 14 (e.g., a blower). However, unlike thoseapparatus previously set forth, the motor speed of the flow generator iscontrolled by a central processing unit (CPU) 136. The apparatus alsoincludes a suitable patient condition sensor means such as a pressuretransducer 138 situated within or near the breathing circuit, i.e., thebreathing mask 22, conduit means 20 or gas flow generator 14. In itsmost general form, the pressure transducer 138 is a differentialpressure sensor capable of detecting selected pressure differentials inthe patient's breathing circuit associated with pressure or pressures ofselected magnitude and/or frequency. A preferred, although notlimitative, embodiment of the pressure transducer 138 is an audiotransducer or microphone. When, for example, snoring sounds occur thepressure transducer detects the sounds and feeds correspondingelectrical impulses to the CPU 136 which, in turn, generates a flowgenerator motor control signal. Such signal increases the speed of theflow generator motor, thereby increasing output pressure supplied to thepatient through the pressure controller 26 and conduit means 20.

As snoring is caused by vibration of the soft palate, it is thereforeindicative of an unstable airway and is a warning signal of theimminence of upper airway occlusion in patients that suffer obstructivesleep apnea. Snoring is itself undesirable not only as it is adisturbance to others but it is strongly believed to be connected withhypertension. If the resultant increase in system output pressure issufficient to completely stabilize the airway, snoring will cease. If afurther snoring sound is detected, the pressure is again incrementallyincreased. This process is repeated until the upper airway is stabilizedand snoring ceases. Hence, the occurrence of obstructive apnea can beeliminated by application of minimum appropriate pressure at the time ofuse.

In apparatus such as that disclosed in U.S. Pat. No. 5,199,424, thefeedback circuit includes means to gradually decrease the outputpressure if an extended period of snore-free breathing occurs in orderto ensure that the pressure is maintained at a level as low aspracticable to prevent the onset of apnea. The feedback circuit of thepresent invention as shown in FIGS. 10 through 15 preferably includessimilar means. This effect can be achieved, for example, by the CPU 136which, in the absence of an electronic signal from the pressuretransducer 138 indicative of snoring, continuously and gradually reducesthe flow generator speed and output pressure over a period of time. If,however, a snore is detected by the first pressure transducer, the CPUwill again act to incrementally increase the output of the flowgenerator.

In use, a patient may connect himself to the apparatus 210 and go tosleep. The output pressure is initially at a minimum operating value of,for example, approximately 3 cm H₂ O gauge pressure so as not to causethe previously mentioned operational problems of higher initialpressures. Not until some time after going to sleep, the patient's bodyrelaxes, will the airway start to become unstable and the patient beginto snore. The pressure transducer 138 will then respond to a snore, orsnore pattern, and via the CPU 136 increase the flow generator motorspeed such that output pressure increases, for instance, by 1 cm H₂ Ofor each snore detected. The pressure can be increased relativelyrapidly, if the patient's condition so requires, to a working pressureof the order of 8-20 cm, which is a typical requirement. An upperpressure limiting device, to be described later herein, can beincorporated for safety. Additionally, for ease of monitoring thevariation over time a parameter such as pressure output can be recordedin some convenient retrievable form and medium (a preferred embodimentof which is also later described) for periodic study by the physician.

If for example in the early stages of sleep some lesser output pressurewill suffice, the apparatus of the present invention will not increasethe pressure until needed, that is, unless the airway becomes unstableand snoring commences no increase in airway pressure is made.

By continuously decreasing the output pressure at a rate of, forexample, 1 cm H₂ O each 15 minutes in the absence of snoring, thepressure is never substantially greater than that required to preventapnea. However, such elevated pressure may be somewhat uncomfortable tothe patient should he suddenly awaken and immediately wish to resumetherapy at a minimum pressure to facilitate has transition back to asleeping state. A preferred approach for alleviating this particularphenomenon is addressed later herein in connection with the discussionof FIG. 12.

Like other feedback type positive airway pressure ventilation apparatusknown to those skilled in the art, the feedback circuit of FIGS. 10-15provides a device which adjusts apparatus output pressure according tovariations in a patient's breathing requirements throughout an entiresleep period. Further, it will be understood that the present inventionas represented in FIGS. 10 through 15 will likewise accommodate variableoutput pressure requirements owing to general improvements ordeteriorations in a patient's general physical condition as may occurover an extended period of time.

Still referring to FIG. 10, it is revealed that the embodiment of theapparatus 210 represented therein, apart from its patient-responsivevariable pressure output capability, may also be provided with rampcontrol circuitry means 104 , 104' of the types possessing thecharacteristics described in detail in connection with the discussion ofFIGS. 7A and 7B. That is to say, apparatus 210 may also include rampcontrol circuitry means connected to the pressure controller 26 foreffecting (1) a first ramp cycle wherein gas flow from the pressurecontroller is initially output at a first pressure and raises with timeto a second pressure, and (2) at least one additional selectivelyactivable ramp cycle. Pursuant thereto, the ramp control circuitry means104, 104' may include, inter alia, means for adjusting the magnitudes ofthe first and second ramp pressures, as well as means for adjusting thedurations and/or pressure patterns of the first and any additional rampcycles. And, like the apparatus of FIGS. 5A the activation of theapparatus 210 as well as its ramp cycles may be achieved throughsuitable manipulation of appropriate manually manipulable actuators,such as buttons, switches, or the like, provided on a remote control106.

FIG. 11 represents an apparatus, herein designated by reference numeral310, which desirably incorporates the features of a feedback typepositive airway pressure ventilation apparatus with a patient sensormeans 107' and sensor means 106' of the types discussed in regard to theapparatus 10' of FIG. 5A. Thus, the apparatus 310 preferably includes apatient sensor means 107' such as a pressure, flow, thermal, audio,optic, electrical current, voltage, force or displacement transducer.The patient sensor means may be situated within or proximate thepatient's breathing circuit which comprises gas conduit 20, gas flowgenerator 14 and a suitable respiratory interface such as respiratorymask 22 and is operable to detect the pressure (and/or absence) of thepatient so as to automatically control activation and deactivation ofthe apparatus. Accordingly, pursuant to a first mode of operation whenthe mask is appropriately positioned over the patient's face, the sensormeans 107' will detect the patient's presence and generate a signal thatis transmitted to the flow generator 14 to activate the apparatus. In asecond operational mode, the patient sensor means may functionexclusively to deactivate the apparatus. Thus, upon removal of the mask,the sensor would fail to detect any conditions indicative of thepatient's presence and generate and transmit a signal to deactivate theapparatus. And, as with the patient sensor means of FIG. 5A, a thirdmodality combines these functions. That is to say, the patient sensormeans 107' may be operable to detect the presence and absence of thepatient and generate a signal to activate the apparatus upon detectionof a condition indicative of the patient's presence, as well as anapparatus deactivation signal upon failure of detecting such a signal,i.e., the patient's absence.

Likewise, the sensor means 106' may function in the manner of itscounterpart, sensor means 106' of FIG. 5A, i.e., as a substitute for amanually manipulable ramp activation button, switch, or the like,provided on a remote control device such as remote control 106 of FIGS.5 and 10. Thus, the sensor means 106' may comprise any suitable sensormeans responsive to predetermined signals consciously produced by thepatient. Again, pursuant to a presently preferred construction, thesensor means 106' comprise a pressure transducer responsive to apressure or pressures of selected magnitude and/or frequency. Forinstance, sensor means 106' may be a microphone located within thepatient's breathing circuit or gas flow system (i.e., in or near thepatient's respiratory interface, associated gas flow conduit or gas flowgenerator) and capable of detecting sound waves of a limited frequencyrange substantially spanning that associated with human speech.Constructed and arranged as such, the transducer would be nonresponsiveto common ambient sounds produced by the patient (e.g., coughing orsneezing), machinery noise, music or animal sounds. Moreover, by beingisolated through its enclosure within the gas flow system, thetransducer 106' would detect only the patient's speech to the exclusionof others in the vicinity or speech emanating from television or radiosources. Upon detection of the patient's speech such as, for example,when the patient awakens and then speaks to initiate a new ramp cycle tofacilitate transition to a sleeping state, the transducer generates andtransmits an activation signal to the ramp control circuitry means104,104' to initiate the desired ramp cycle. The ramp activation sensormeans 106' may alternatively be operable to begin a ramp cycle inresponse to detection of a predetermined pattern of inhalations and/orexhalations or other conscious actions by the patient.

FIG. 12 reveals an apparatus 410 constructed according to a furtherembodiment of the present invention. Like apparatus 210 and 310,apparatus 410 is of the feedback type whose operation has been generallydiscussed above in connection with FIG. 10. Apparatus 410 additionallyincludes reset circuitry means or "reset circuit" 140. The reset circuit140 permits the patient (if suddenly awakened, for instance) toinstantaneously reset the system output pressure to a predeterminedreduced pressure whereupon the treatment may then proceed as it didprior to reset. An advantage attendant to the ramp control circuitrymeans 104, 104' and the reset circuit 140 is that they both afford thepatient the opportunity to immediately respire against a reducedpressure once awakened, thereby enhancing comfort and transition back toa sleeping state. The following example will assist the reader inconceptualizing the value of these features.

Suppose that the patient is experiencing feedback type positive airwaypressure therapy and awakens for whatever reason. It will be appreciatedthat under such circumstances the patient will, upon awakening, likelybe experiencing a somewhat elevated airway pressure, even if theventilation apparatus were functioning in the gradually decreasingoutput pressure mode associated with an extended period of snore-freebreathing. To achieve a comfortable output pressure conducive to thepatient's falling back to sleep, the patient would either have to waituntil the output pressure reaches a comfortable level (which may take upto an hour or longer). Alternatively, the patient would be required todeactivate the entire apparatus, perform any system checks, e.g.,leakage tests, which may be required to assure proper functioning of theapparatus and wait until the apparatus returns to its normal operationalmode.

In accordance with the present system, however, the patient merelyoperates a reset circuit actuator 142 to effect activation of the resetcircuit 140 and thereby instantaneously reset the apparatus 410 toresume therapy. Consistent with other embodiments of the invention thusfar described, the reset circuit actuator 142 may assume the form for amanually manipulable button, switch, or the like, provided directly onthe apparatus housing or on a remote control such as remote control 106of FIGS. 5 and 10. If constructed in such a fashion, the reset circuitactuator desirably will have a substantially different physicalconfiguration than the apparatus activation and ramp activationactuators whereby it can be readily identified by the patient by eithersight or touch. As an alternative construction, the reset circuitactuator may be a sensor means similar to sensor means 106' of FIGS. 5Aand 11.

Unlike the ramp control circuitry means 104, 104' however, the resetcircuit 140 of FIG. 12 permits the patient, when such is desired ornecessary, to more rapidly receive the full benefits of the positiveairway pressure therapy since therapy resumes instantaneously uponreset. As will be appreciated, the reset circuit 140 rather than theramp control circuitry means 104,104 is more likely to be activated by apatient who generally experiences little difficulty in falling back tosleep once awakened.

A further embodiment of the present invention is shown in FIG. 13.Again, there is provided a feedback type positive airway pressureventilation apparatus, reference numeral 510, in this instance alsoincluding a safety circuit 144 comprising an adjustable maximum pressuresetting control 146 and an adjustable minimum pressure setting control148.

The safety circuit 144 allows the manufacturer, the patient or hisoverseeing health care professional to selectively establish minimum andmaximum system output pressures below and above which the system willnot dispense pressurized gas. The minimum pressure will, of course, beat least zero and, preferably, a threshold pressure sufficient tomaintain pharyngeal patency during expiration. The maximum pressure, onthe other hand, will be some pressure somewhat less than that whichwould result in over-inflation and perhaps rupture of the patient'slungs. The safety circuit functions differently than the pressurecontrols 116 and 122 of the ramp control circuitry means 104, 104'. Thatis, instead of establishing lower and upper prescription pressures to beapplied during normal usage of the apparatus, it sets absolute minimumand maximum fail-safe output pressure limits which are not to beexceeded, and therefore potentially cause physical harm to the patientin the event the other system components, e.g., the feedback circuit, orthe prescription pressure controls of the ramp control circuitry means,malfunction.

The embodiment according to FIG. 14, which is generally identified byreference numeral 610, includes the aforesaid pressure feedback circuitas well as system data storage and retrieval means 150 and a therapydelay circuit 152. Apparatus 610 represents an embodiment of the instantinvention which finds primary application in the "clinical" environment,i.e., in a sleep study of the patient performed in a hospital, clinic orlaboratory.

System data storage and retrieval means 150 may within the scope of thepresent invention comprise any suitable computer memory into whichinformation can be read and from which information can be written.Representative, although not limitative, embodiments of the system datastorage and retrieval means may therefore include a random access memory(RAM), magnetic tapes or magnetic disks which may be incorporated into astand-alone personal computer, mainframe computer, or the like (notillustrated). In cooperation with the system data storage and retrievalmeans 150, the therapy delay circuit 152 permits a patient's sleepdisorder to be diagnosed and treated during a single sleep study. Stateddifferently, in a marked departure from other clinicaldiagnosis/treatment systems presently known to the inventors to beemployed in the subject art, the apparatus 610 of FIG. 14 can undermany, if not all, circumstances enable diagnosis and treatment of thepatient's respiratory-related sleep disorder in a single night at thesleep study facility.

In this connection, the typical practice has been for the patient toundergo two sleep studies at an appropriate observation facility such asa hospital, clinic or laboratory. The first night is spent observing thepatient in sleep and recording data associated with selectedphysiological parameters such as oxygen saturation, chest wall andabdominal movement, air flow, expired CO₂, ECG, EEG, EMG and eyemovement. This information can then be interpreted to diagnose thenature of the sleeping disorder and confirm the presence or absence ofapnea and, where present, the frequency of apneic episodes and extentand duration of associated oxygen desaturation. Apneas can be identifiedas obstructive, central or mixed.

The second night is spent with the patient undergoing positive airwaypressure therapy. When apnea is observed the pressure setting isincreased as required to determine the maximum pressure necessary toprevent apnea. For a given patient in a given physical condition therenormally will be found different minimum pressures for various stages ofsleep in order to prevent occlusions.

In order to condense the present practice of a two night sleep studyinto a single night, the therapy delay circuit 152 of the instantinvention is operable to suppress the application of positive airwaypressure therapy for any desired period of time, e.g., several hours,while the system data storage and retrieval means compile data from oneor more data input lines 154 which communicate data associated with thepatient's physiological parameters necessary for proper diagnosis of thepatient's particular sleep disorder. Once sufficient data is recorded inthe system data storage and retrieval means 150, system controladjustments based upon the data including, but not limited to, absolutemaximum and minimum system output pressures (FIG. 13), and rampprescription pressures, durations and patterns (FIGS. 10 and 11), may beinputted as appropriate and the therapy delay circuit 152 may beswitched from its therapy suppression mode to a therapy applicationmode, whereby treatment specifically responsive to conditions observedduring diagnosis may be effectively implemented in a single night in thesleep study facility. The terms "suppress" and its conjugates in thepresent context will be understood to mean limiting pressure output ofthe apparatus from a value of at least zero and up to a predeterminedvalue which is usually below a normal therapeutic output pressure.

An exemplary construction of the therapy delay circuit 152 isillustrated in FIG. 14. The circuit 152 may include a three-positionswitch 156 (shown in its open or "OFF" position) which preferably isadapted for use in an "automatic" therapy delay or suppression mode ofthe circuit. Switch 156 is electrically connected to an adjustable timer158. Timer 158 may be infinitely adjustable for any time period fromabout 0 to 8 hours. The timer is, in turn, connected to andautomatically controls a two-position switch 160 (also shown in its openor "OFF" position).

When it is desired to operate the therapy delay circuit in the automaticmode, the clinician or other health care professional monitoring thepatient's sleep study adjusts the timer 158 to a desired therapy delayperiod, e.g., 3 to 4 hours, and positions the switch 156 to the"AUTOMATIC ON" position. During the established therapy delay period thepatient falls asleep, the feedback circuit is suppressed and the systemdata storage and retrieval means 150 compiles physiological datagathered from the patient and transmitted by data input lines 154. Atthe expiration of the therapy delay period, any system pressure andother parameters may be appropriately adjusted by the clinician and thetimer automatically closes switch 160, i.e., places it into its "ON"position, to send therapy activation signal 162 to the flow generator 14to cause the feedback circuit of apparatus 610 to provide the patientwith ventilation therapy particularly suited to his sleep disorderrequirements.

Simultaneously, a signal 162' is transmitted to the system data storageand retrieval means 150. The signal 162' serves as a control signalwhich may be selected by the apparatus operator to either deactivatemeans 150 during therapy or to cause means 150 to collect data from thepatient data input lines 154, flow generator 14, pressure controller 26and/or other selected sources during therapy. Upon deactivation of theapparatus following completion of a therapy session both switches 156and 160 automatically return to their open or "OFF" positions.

Switch 156 may also be switched into a "manual" mode whereby the timer158 and switch 160 are bypassed. Thus, when the switch 156 is placedinto the "MANUAL ON" position, such as when the apparatus operator issatisfied that sufficient diagnostic data has been compiled, signals 162and 162' are respectively transmitted to the flow generator 14 andsystem data storage and retrieval means 150.

Although, as noted above, the system data storage and retrieval means150 and delay therapy circuit 152 find their primary usage in the sleepstudy facility, such components may also be incorporated into thepatient's home ventilation apparatus as well. Under such circumstances,the patient can, with proper instruction, personally monitor theprogress or deterioration of his therapy over a period of time andadjust the therapy parameters as necessary. In either case, provision ofthe system data storage and retrieval means and therapy delay circuitenable the user to spend less time in the sleep study facility or underdirect supervision of a professional health care worker, hence reducingtherapy cost and inconvenience.

FIG. 15 represents a further embodiment of the present invention.According to this embodiment, the positive airway pressure apparatus(reference numeral 710) comprises the above-described feedback circuitand a minimum system leakage assurance circuit 164, the function ofwhich is to assure that the system discharges a minimum leakage flowduring therapy, i.e., when the patient is asleep or attempting to fallasleep. The minimum system leakage assurance circuit 164 desirablycomprises an adjustable leakage test pressure control 166, an adjustablepre-therapy control 168, an adjustable timer 170 and a three-positionswitch 172. The switch 172 is responsive to the timer 170 and triggersthe leakage test pressure control 166 to transmit a signal 174 causingthe apparatus 710 to output a preset leakage test pressure. The switchis also operable to trigger the pre-therapy pressure control 168 totransmit a signal 176 causing the apparatus to output a presetpre-therapy pressure. The preset leakage test pressure is a relativelyhigh pressure and may, for instance, be the peak pressure output by theapparatus during the previous night or some other desired pressure.Similarly, the pre-therapy pressure is a relatively low pressure and maybe the minimum pressure output by the apparatus during the previousnight or some other pressure.

Using the timer 170, after the apparatus is activated the system willoutput the leakage test pressure to temporarily overpressurize the gasflow circuit for some preselected period of time. This time period (e.g.several seconds) would normally be sufficient for the patient toproperly position and seal the respiratory interface, e.g., mask 22, onhis face and adjust any gas conduit connections such that system leakageflow is brought to a minimum. After expiration of the prescribed periodof time, the timer triggers the switch 172 to activate the therapypressure control 168 to transmit signal 176, thereby causing the systemto output the selected pre-therapy pressure for a specified durationalso established by the timer. After expiration of the designated timefor pre-therapy pressure application, the timer then urges the switch toassume a neutral or "OFF" position whereby the apparatus outputs itsdesignated positive airway pressure therapy.

An advantage of such an arrangement is that by temporarilyoverpressurizing the gas flow circuit prior to treatment, unwantedsystem leaks can be discovered and sealed before the patient fallsasleep. Hence, leakage flow (or average system flow) and its associatedpressure can be minimized while the patient sleeps, thereby enhancingpatient comfort. In lieu of or addition to the timer 170, the minimumsystem leakage assurance circuit 164 may also include a low leakdetector 178. The low leak detector detects whether the system, underthe application the leak test pressure (which may be programmed to beoutput automatically upon apparatus activation), outputs a leakage flowless than a predetermined minimum leakage flow. If a sufficiently lowleakage flow is detected, the low leak detector automatically overridesthe timer (if present) and triggers the pre-therapy pressure control 168to cause the system to output the specified pre-therapy pressure for apreset time and then output the appropriate therapy pressure.

Similarly, in addition to or in lieu of the timer 170 and/or the lowleak detector 178, the minimum system leakage assurance circuitry mayinclude a manual override 180, e.g., a button, switch orpatient-responsive transducer, which responds to patient initiatedcommands to override the timer and/or low leak detector (if present).

For clarity of illustration and description, the various apparatuscontrol circuits of FIGS. 10 through 15 are depicted as beingindividually associated with the positive airway pressure feedbackcircuits of those figures. However, under many, if not all,circumstances there will in fact be more than one of the ramp controlcircuitry means 104, 104', reset circuit 140, safety circuit 144,therapy delay circuit 152 (and system data storage and retrieval means150), and minimum system leakage assurance circuit 164 present in theventilation apparatus. Indeed, it is contemplated that these circuitsmay coexist in any combination with one another, as well as with otherventilation control components known to those skilled in the art.

Although the invention has been described in detail for the purpose ofillustration, it is to be understood that such detail is solely for thatpurpose and that variations can be made therein by those skilled in theart without departing from the spirit and scope of the invention exceptas it may be limited by the claims.

What is claimed is:
 1. Apparatus for delivering pressurized gas to an airway of a patent, said apparatus comprising:a gas flow generator that provides a flow of gas; a conduit operatively coupled to said gas flow generator, said conduit being adapted to deliver said flow of gas to an airway of a patient; a pressure controller cooperable with said gas flow generator to provide said flow of gas within said conduit at selectively variable pressures; reset means for permitting a patient to substantially instantaneously reset said pressure controller to provide said flow of gas at a predetermined reduced pressure after which said pressure controller resumes provision of said flow of gas in a manner substantially similar to that provided prior to said reset; and safety means for preventing said pressure controller from providing said flow of gas at a pressure above a predetermined maximum pressure.
 2. Apparatus for delivering pressurized gas to an airway of a patient who is breathing in repeated breathing cycles, each cycle including an inspiratory phase and an expiratory phase, said apparatus comprising:a gas flow generator that provides a flow of gas; a conduit operatively coupled to said gas flow generator, said conduit being adapted to deliver said flow of gas from said gas flow generator to an airway of a patient; a pressure controller cooperable with said gas flow generator to provide said flow of gas within said conduit at selectively variable pressures; a detector that detects a rate of flow of gas between said gas flow generator and an airway of a patient; processor means cooperable with said detector for providing flow rate information of said flow of gas between said gas flow generator and an airway of a patient, said flow rate information including a first indicia corresponding to an instantaneous flow rate of said gas and a reference indicia approximating an average flow rate of said gas; decision means operable to utilize said first indicia and said reference indicia to identify an occurrence of at least one of said inspiratory phase and said expiratory phase, said decision means being cooperable with said pressure controller to control variation of said pressure of gas responsive to identification of an occurrence of at least one of said inspiratory phase and said expiratory phase; ramp control means, operatively connected to said pressure controller, for effecting (1) a first ramp cycle, wherein said gas flow from said pressure controller is initially output at a first pressure and raises with time to a second pressure, and (2) at least one additional ramp cycle selectively activatable through conscious action of a patient; and safety means for preventing said pressure controller from providing said flow of gas at a pressure above a predetermined maximum pressure.
 3. Apparatus for delivering pressurized gas to an airway of a patient who is breathing in repeated breathing cycles, each cycle including an inspiratory phase and an expiratory phase, said apparatus comprising:a gas flow generator that provides a flow of gas; a conduit operatively coupled to said gas flow generator, said conduit being adapted to deliver said flow of gas from said gas flow generator to an airway of a patient; a pressure controller cooperable with said gas flow generator to provide said flow of gas within said conduit at selectively variable pressures; a detector that detects a rate of flow of gas between said gas flow generator and an airway of a patient; processor means cooperable with said detector for providing flow rate information of said flow of gas between said gas flow generator and an airway of a patient, said flow rate information including a first indicia corresponding to an instantaneous flow rate of said gas and a reference indicia approximating an average flow rate of said gas; decision means operable to utilize said first indicia and said reference indicia to identify an occurrence of at least one of said inspiratory phase and said expiratory phase, said decision means being cooperable with said pressure controller to control variation of said pressure of said gas responsive to identification of an occurrence of at least one of said inspiratory phase and said expiratory phase; ramp control means, operatively connected to said pressure controller for effecting (1) a first ramp cycle wherein said gas flow from said pressure controller means is initially output at a first pressure and raises with time to a second pressure, and (2) at least one additional selectively activatable ramp cycle; means, associated with said ramp control means, for adjusting a magnitude of said first pressure; means, associated with said ramp control means, for adjusting a magnitude of said second pressure; means, associated with said ramp control means, for adjusting a duration of said first ramp cycle; means, associated with said ramp control means, for selecting a fraction of an adjusted duration of said first ramp cycle as established by said means for adjusting said duration of said first ramp cycle; means, associated with said ramp control means, for adjusting a duration of said at least one additional ramp cycle; means, associated with said ramp control means, for establishing a predetermined pattern of pressure output from said pressure controller means during progression from said first pressure to said second pressure; remote control means for selectively activating said apparatus and said ramp control means; and safety means for preventing said pressure controller from providing gas flow at a pressure above a predetermined maximum pressure.
 4. Apparatus for delivering pressurized gas to an airway of a patient, said apparatus comprising:a gas flow generator that provides a flow of gas; a conduit operatively coupled to said gas flow generator, said conduit being adapted to deliver said flow of gas to an airway of a patient; a pressure controller cooperable with said gas flow generator to provide said flow of gas within said conduit at selectively variable pressures; ramp control means operatively connected to said pressure controller for effecting (1) a first ramp cycle wherein said gas flow from said pressure controller means is initially output at a first pressure and raises with time to a second pressure, and (2) at least one additional ramp cycle selectively activatable through conscious action of a patient; means, associated with said ramp control means, for adjusting a duration of said first ramp cycle; means, associated with said ramp control means, for selecting a fraction of an adjusted duration of said first ramp cycle as established by said means for adjusting said duration of said first ramp cycle; and safety means for preventing said pressure controller from providing gas flow at a pressure above a predetermined maximum pressure.
 5. Apparatus for delivering pressurized gas to an airway of a patient, said apparatus comprising:a gas flow generator that provides a flow of gas; a conduit operatively coupled to said gas flow generator, said conduit being adapted to deliver said flow of gas to an airway of a patient; a pressure controller cooperable with said gas flow generator to provide said flow of gas within said conduit at selectively variable pressures; ramp control means operatively connected to said pressure controller means for effecting (1) a first ramp cycle wherein said gas flow from said pressure controller means is initially output at a first pressure and raises with time to a second pressure, and (2) at least one additional selectively activatable ramp cycle; means, associated with said ramp control means, for adjusting a magnitude of said first pressure; means, associated with said ramp control means, for adjusting a magnitude of said second pressure; means, associated with said ramp control means, for adjusting a duration of said first ramp cycle; means, associated with said ramp control means, for selecting a fraction of an adjusted duration of said first ramp cycle as established by said means for adjusting said duration of said first ramp cycle; means, associated with said ramp control means, for adjusting a duration of said at least one additional ramp cycle; means, associated with said ramp control means, for establishing a predetermined pattern of pressure output from said pressure control means during progression from said first pressure to said second pressure; remote control means for selectively activating said apparatus and said ramp control means; and safety means for preventing said pressure controller means from providing gas flow at a pressure above a predetermined maximum pressure. 